Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps located above the motor. When energized, the motor provides torque to the pump, which pushes wellbore fluids to the surface through production tubing. Each of the components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment.
Components commonly referred to as “seal sections” protect the electric motors and are typically positioned between the motor and the pump. In this position, the seal section provide several functions, including transmitting torque between the motor and pump, restricting the flow of wellbore fluids into the motor, protecting the motor from axial thrust imparted by the pump, and accommodating the expansion and contraction of motor lubricant as the motor moves through thermal cycles during operation.
In certain applications, an auxiliary pump can be connected below the motor. Auxiliary pumps can be advantageously employed in applications where a portion or all of the pumping system is located below the perforations in the wellbore. Such a system is disclosed in U.S. Pat. No. 6,666,269, entitled “Method and Apparatus for Producing Fluid From a Well and For Limiting Accumulation of Sediments in the Well,” issued Dec. 23, 2003 to Bangash et al. and assigned to the owner of the present application (the “Bangash '269 patent”). As disclosed in the Bangash '269 patent, the auxiliary pump lifts fluids and sediment produced by the formation to a production pump located above the motor. The production pump pushes the fluid and sediment out of the well through production tubing. The auxiliary pump increases fluid flow around the motor, which moderates the temperature of the motor during operation.
The discharge head of the auxiliary pump in the Bangash '269 patent is connected directly to the motor. The auxiliary pump discharge head includes a mechanical seal designed to prevent wellbore fluids from migrating through the auxiliary pump discharge into the motor. Although generally effective, there is a need for alternative designs that can be used to provide additional protection to the motor in certain applications. It is to this and other needs that the present invention is directed.